Atomic Structure

Question 1

Define relative atomic mass

Answer 1

The average mass of an atom of an element
Compared to 1/12th the mass of an atom of carbon 12

Question 2

Give two reasons why it’s necessary to ionise the isotope of an element

Answer 2

So they can be accelerated
Ions create a current when hitting detector

Question 3

Describe how molecules are ionised in electrospray ionisation

Answer 3

Sample is dissolved in volatile solvents
Injected through a needle at high voltage
Each molecule gains a proton

Question 4

Describe how ions are formed in time of flight

Answer 4

A high voltage is applied to a polar substance
The sample molecule gains a proton

Question 5

Copper has two isotopes 63-Cu and 65-Cu. The relative atomic mass of copper is 63.5.
Calculate the percentage abundances of these two isotopes.

Answer 5

63.55 = yx63 + (1-y)x65
63.55 = 63y +65 -65y
63.55 = 65 -2y
2y = 1.45
y = 0.725